1. Field of the Invention
The invention relates to a fuel injection control device and fuel injection control method that are applied to an internal combustion engine having a fuel injection valve that directly injects fuel into a cylinder in order to execute fuel injection control.
2. Description of Related Art
There is known a fuel injection control device for a diesel engine that includes fuel injection valves that directly inject fuel into corresponding cylinders (for example, see Japanese Patent Application Publication No. 2011-190725 (JP 2011-190725 A)). When each fuel injection valve is manufactured, there may occur an individual difference in injection characteristic. Therefore, before each fuel injection valve is assembled to a diesel engine, an initial value of a learned value (hereinafter, initial learned value) for compensating the individual difference of each fuel injection valve is preset through a test carried out with the use of a testing device. Specifically, the corresponding fuel pressure sensor is used to detect a manner of fluctuation of the fuel pressure inside each fuel injection valve with the injection of fuel by the fuel injection valve. And then the tendency of deviation of a temporal waveform of a fuel injection rate that is calculated from the detected manner of fluctuation of the fuel pressure (hereinafter, detected temporal waveform) with respect to a basic temporal waveform on the basis of the result of comparison between the detected temporal waveform and the basic temporal waveform. Then, the initial learned value for correcting a control value of each fuel injection valve is set on the basis of the tendency of deviation. By using the initial learned value in fuel injection control over the diesel engine, an individual difference of each fuel injection valve at the time of manufacturing is compensated, and fuel injection is accurately carried out through each fuel injection valve.
On the other hand, the injection characteristic of each fuel injection valve varies due to aged deterioration through engine operation. Then, the fuel injection control device described in JP 2011-190725 A includes the fuel pressure sensor that detects a fuel pressure inside the corresponding fuel injection valve provided in each cylinder, calculates the above-described detected temporal waveform from the detected value of the fuel pressure sensor during engine operation, and calculates the tendency of deviation of the detected temporal waveform with respect to the above-described basic temporal waveform from the result of comparison between the detected temporal waveform and the basic temporal waveform. Then, the learned value for correcting the control value of each fuel injection valve is updated on the basis of the tendency of deviation (hereinafter, learned value updating process). By executing such learned value updating process, even when there occurs an individual difference due to aged deterioration in each fuel injection valve, fuel injection is accurately carried out through each fuel injection valve.
When a detected value of the corresponding fuel pressure sensor has suddenly varied through, for example, superimposition of noise due to disturbance, if the tendency of deviation, which is calculated from the result of comparison between the detected temporal waveform and the basic temporal waveform, is directly used to update a learned value, the learned value may be updated to an inappropriate value. Then, the tendency of deviation is reflected at a predetermined reflection rate at the time of updating the learned value, and the learning rate of the learned value is decreased by reducing the predetermined reflection rate. By so doing, even when a detected value of the corresponding fuel pressure sensor has suddenly varied, the learned value is updated to an appropriate value.
When an initial learned value is calculated through a test carried out with the use of the testing device before each fuel injection valve is assembled to a diesel engine, an environment in which each fuel injection valve is placed may be different between the testing device and an actual diesel engine. Therefore, even if an initial learned value having a high reliability is set through a test carried out with the use of the testing device, the initial leaned value may not always be an appropriate value by which it is possible to compensate for the individual difference of each fuel injection valve in a state where the fuel injection valve is assembled to an actual diesel engine. In the above-described fuel injection control device, the learning rate of the learned value is decreased. Therefore, it may not be possible to update a learned value to an appropriate value within an ordinary test operation period in which test operation for a diesel engine is carried out in a manufacturing factory or a maintenance factory, and it may be necessary to extend the test operation period.
The above-described possibility not only applies to a fuel injection control device for a diesel engine but also mostly commonly applies to a fuel injection control device for a gasoline engine that includes a fuel injection valve that directly injects fuel into a cylinder. In addition, it is not limited to a configuration that an initial learned value is preset for each fuel injection valve, but it may also mostly commonly occur in a configuration that an initial learned value is not set.